Note: Star vs the Forces of Evil belong to Disney and Sonic the Hedgehog belong to Sega. I don't own anything. I hope you like my fanfiction story and since is my very first fanfiction, my writing may not be 100% perfect. Now the left of, Sonic and Knuckles fought Big Arms and took down the Wing Fortress, and Tails work with Pony Head to take down Seth and help Star and Marco but Seth has stolen our heroes' emeralds and reveal their plot and some lore about Seth's disappearance and how he met Eggman. Now the story continues and hopefully our heroes have a plan to find Neo Scrap Brain Zone and save the day before Eggman's plan is set in motion.

Sonic and Star in Adventure in Mewni
Chapter 7 A new plan

Star feels totally defeated, sitting in a chair in King Pony Head's throne room, she's lost in thought as Seth's haunt her mind will our heroes help King Pony head, who is now conscience again, organize to clean up the mess Eggman's and Seth's armies left behind and while Tails sit in another chair next to Star as the fox tinker with the handheld hologram transmitter they got from Rasticore in hope of finding some information about the where abouts of Eggman's secret base.

"Hey Star, is everything ok?" Asked Marco pulling up a chair to sit beside Star, he noticed that something is bothering her.

"I destroy the Realm of Magic to save everyone, but I let loose a very ancient evil from my family's mess up past. It feels like this is all my fault Marco."

"Star, you didn't know, in fact I didn't know and I was there when that Realm of Magic got destroyed, Seth must have been far enough to see and grab the wand before when we were distracted or something like that."

"But it feels like I just repeated history, we just learn that Seth's disappearance because of Comet Butterfly banishing him into the Realm of Magic just before Toffee...put her in a wooden nightgown? You get the idea Marco. Well that least we know."

"But Star, it was also a Chaos Emerald that appeared that the right moment, that was just Murphy's Law at play." Chimed in Tails, and continued "I understand how your feeling, I was in that spot too, I thought I was a burden to Sonic, but in our last adventure, Sonic reminded me that I'm not and he also said that he's always proud of me to be his friend."

"Star, for the short time, we got to know each other, You did the right thing for destroying the Realm of Magic to save your friends and family."

"Tails is right, and like Sonic and Tails, I'm proud of being you friend, you're not a burden." Said Marco as he hug his friend which make her feel better.

"Oh thanks guys, now let's finish this and stop those two from using the emeralds and get back the wand."

"Good thing too." Sonic walk up to them seeing that the situation has resolve itself "Tails, I glad you told Star what I told you back on the Starfall Islands and I'm proud at that, but did you managed to locate..."

"Neo Scrap Brain Zone? yup, I was going to tell you before I decide to help Star." then Tails activated the transmitter's hologram to show a map with the location of Eggman's base.
"Eggman hidden his base in the mountains and I can get us there with the M.E.D.E.L."

"But Tails, Seth took our emeralds?"

"Not all of them." Then Tails pull out the emerald Star gave him earlier today.
"Oh right I totally forgot all about it, which means, they got 6 emeralds along with the wand and the Master Emerald." realized Star.

"Oh I bet that egg head and lizard are real mad right now."

"That's right."

Then Sonic give Tails a thumbs up and then he turn to face Star.

"Star, thanks for you and your friends help, but this is where we part ways. Eggman's base will be too dangerous from this point."

"Too dangerous?" Said Star, "Sonic, I know Eggman is your villain and all, but Seth, I think he has he's own plan which both everyone, even Eggman, in deep trouble."

"But Star, no doubt there will be traps that could kill any normal person, I won't want anyone's lives on the line."

"But with Seth, everyone lives are already on the line."

"She's right Sonic. I see Seth's fighting style and he could have won if I didn't interfere."

"Oh hedgehog." cry out Pony Head as she hover towards Sonic.

"Look, I can see you want to protect my friends and all, but your friends, Tails and Knuckles, come with you to our world, to stop an evil lizard and an egg-shape man from whatever they're planning. They know the risks and so does Star and Marco."

"Yeah but..."

"No buts, you see these two also risk their lives even before you show up, I am not saying you do a terrible job, you do a great job then you took down that airship, but all I'm saying is that once Star do something, she won't stop to protect her friends, her family, and her world just like you and even though she no longer have magic, that won't stop her, so she can handle whatever those two jerks could throw."

Pony Head's argument was...hard to understand, but Sonic get what she's trying to say.

"She's got a point Sonic" chimed in Knuckles who heard everything. "We seem her determination to save her parents back in the Monster Temple."

Sonic went silence for a few minutes until he turn to Star and Marco and said, "ok but it's not me to decide, since this is Star's world so it's your decision. I'll let you talk with Marco.

"Thanks Sonic" then Star gave Sonic a handshake.

Meanwhile back in Neo Scrap Brain Zone.
"I CAN'T BELIEVE THIS"
Eggman was angry at Seth in the command room when he founded out that there's only 2 emeralds in Star's bag which Seth has stolen back in Cloud Kingdom.

"On the bright side, we cause a mass panic in the streets of Echo Creeks." Then turn on the news on the main computer's screen which the news headlines reads, 'flying airship flies over Echo Creek and attack the Cloud Kingdom.' "I think the message is clear even though we lost Wing Fortress and our one surprise attack. Plus, I think 6 Chaos Emeralds will be enough for our plans to create the most powerful super army."

"True, plus the Death Egg Robot's modifications are complete and with the wand finally restored thanks to the Master Emerald and the remaining Chaos Emeralds, the modification will manipulate the wand's new energy to turn my robot mech into a giant super invincible armor and once we destroy those annoying pest, I can use that energy to turn my army and your army into super soldiers."

Suddenly the alarm went off and the main computer said in a female robot voice, "ALERT INTRUDERS HAS ENTERED NEO SCRAP BRAIN ZONE PERIMETERS" and repeats. Eggman ran up and type on the computer to pull up a live security camera showing Sonic and his friend along with Star and Marco exiting it.

"What?! How did they find us so fast? Oh never mind, all hands to battle." Then Eggman ran out of the command room to get ready his mech for the final battle. However, Seth just stares at the screen, "It's time to make my move, I'll let that egg head do most of the work." Then the leader of the Septarian Army just walk out of the room unfazed.

Meanwhile back to our heroes, after Star and Marco decided to go with Sonic and his friends to finish what they started since the very began of this adventure, there stare in horror to see that Eggman's base is a giant, polluted industrial complex made of light and dark gray metallic building. Dozens of various blinking red, purple, green and yellow lights visible in the distance and a giant egg shape building at the center of the zone sinisterly looming over our heroes.

"This is horrible, this place is polluting the surrounding mountains." Marco said in horror "I'm glad we convince Pony Head to stay behind."

"Ok," began Sonic, "if this place is based on the original back on Mobius, no doubt this place will have the same traps, so be careful. so let me take the lead this time, Tails and Knuckles you stay with Star and Marco and help them get through this metallic gauntlet of a zone. By now we may have triggered the proximity alarm so we could facing a whole bunch of baddies so be careful."

Meanwhile back to Monster Temple. Janna, Pony Head, Buff Frog, Moon and River are having a conversation with a pale skin woman with poofy teal hair, mauve eyes and wore a gothic dress and holding a dark purple umbrella and her husband who is a buff, size shifting with red skin covered in darker red tiger like stripes, four yellow eyes with slitted pupils and wore business-like clothes while hold a hybrid baby in his right arm.

"So you saw the news?"

"Why of course Moon, 3 weeks ago Mewni and Earth fused into New Mewni after destroying the Realm of Magic, and now we got an alien invasion what could destroy all of our hard work of rebuilding along with a rouge Septarian Army lead by Seth who turned out to be still alive working with this Dr. Eggman." said the women with concerned on her face.

"Eclipsa, no one could have predicted that someone from another world without using magic in a way to reach our world."

"Alright calm down you two," said Eclipsa's husband, Globgor, "besides did you say a hedgehog, a fox, and an echidna are on our side along with Star who are at Neo Scrap Brain Zone which we don't know where."

"Hey, I didn't get a good look at that map." Pointed out Pony Head "but my daddy is ready to launch his own attack on Eggman's base."

"Chill out everyone," Chimed in Janna, "I secretly place a tracker into Marco's jacket" then pull out her tracker app on her phone, "they're in the center of some mountains."

"Sweetie," began Eclipsa to Globgor, "let's go help Star."

Back to our heroes. They finally reach the center of the zone in record time, but a whole lot of robots and Septarian Warriors are waiting for them.
"Tails, Knuckles, Sonic Overdrive Team Blast."

"Right." Tails and Knuckles agree, and they rush in towards the bad guys. Knuckles grabs onto Tails by his feet, who is also holding onto Sonic's feet and begins swinging them around to gain momentum.
The Septarian watch in confusion and Star and Marco stare in awe as Knuckles lets go of Tails who then kicks Sonic into the air while Sonic is surrounded by a red aura and yelled "Blast away!" and unleashes a massive Light Speed Atack, zooming around in the air at astounding speeds and striking Septarian Warriors and Eggman's robots.

Seconds later, Sonic lands on the ground as Septarian fell to the ground unconscious and robots exploding everywhere. "Ok that was amazing." Said Marco as he and Star ran up to help Sonic and friends clear out the remaining enemies. But before our heroes could even continue the fight, most of the Septarian, after seeing the Sonic Overdrive, decided to drop their weapons and flee.

"I did not sign up for this, I'm out of here" said a Septarian as he drop his spear and ran along with the remaining warriors and with no Septarian support, the Badniks, Eggman's robots, began to retreat inot the egg-shaped building. Knuckles sense something familiar, somewhere deep within the center of Eggman's base of operations, he sense the Master Emerald.

"The Master Emerald, it's here, I can sense it, along with the 6 emeralds, and one other."
"That must be the wand." Said Star "we're close. But what if Eggman did find a way to recreate parts of Solaria's spell to create an invincible robot?"

"Sonic, do you remember on the ARK when I use the Master Emerald to stop the Chaos Emeralds?"

"Yeah, how could I forget."

"Well since the wand's energy is from the Master Emerald, maybe I can use the Master Emerald to not only stop the Chaos Emeralds, but I could also stop the wand too since it's energy is given from the Master Emerald. It worked on the ARK and it could work again. But I need to make physical contact with it.

"Alright Knuckles, if you say it could work, I'm counting on you." Sonic gave the echidna a thumb up. Then suddenly Tails' M.E.D.E.L began beeping like crazy which forces Tails to take a look and what he found gave him a shock.

"Sonic, my device located the Master Emerald?! It's in the center of this building."

"But you say you couldn't locate the Master Emerald before?"

"I can't explain it, it just happened on its own."

"Well, no time to figure it out, we got two villains to stop." our heroes agreed to that, any minute Eggman gets closer to complete his plan. So, they rush into the base and battle their way against enemies while avoids traps as they go deeper into Eggman's base of operations. Finally, after a hour of going through the second part of the zone which felt like something out of a video game, our heroes reach a giant, metal doors and a large sign above the doors reads 'Master Emerald Generator Room.'

"Taking a guess here, but I think this is where they are holding the Master Emerald in." Said Sonic, then suddenly the metal doors opened automatically and show a giant round room with a dome-shaped roof and in the center of the room, a metal version of the Master Emerald altar which holds the Master Emerald on top.

"The Master Emerald." Knuckles cry out as Marco yelled in amazement. "That is one big gemstone!"
The team of heroes rush in towards the metal altar and Sonic sense that something's not right let's Knuckles, Star, Marco, and Tails go ahead of him. As most of them step on the altar, an two force fields activated forming a small dome surrounding the altar, trapping Star, Tails, Marco, and Knuckles in between, preventing them from reaching the Master Emerald and preventing Sonic who is on the outside of the force field dome to reach his friends. "I knew it was too easy" shouted Sonic "Is everyone alright?"

"We're fine Sonic" Tails replied then a few feet behind Sonic, a giant hidden trap door open and rising out is the Death Egg Robot, Sonic noticed that this one has a gold, silver and black color scheme instead of its usual red, yellow, and black.

"You got here faster than usual Sonic the Hedgehog." Eggman spoke through the speakers.

"The Death Egg Robot again, how many time you use it, like 4, 6 times?"
"You know what, I have listed to your insulting jokes long enough, but I'm in a happy mood right now so I'll let you attack first this time. Go right ahead Sonic."

"Be careful Sonic whispered Tails as Star, Marco and Knuckles watch behind, "I think it's a trap."
"Only one way to find out." Whispered Sonic while smiling, then Sonic spin dash and jump hitting the Death Egg Robot and landed back on the ground, but there was no damage done on the robot, not even a dent.

"What?" shouted Sonic and Eggman laughs evilly.
"HAHAHAHA, yes, the modifications has work. With the wand installed in this robot along with the 6 Chaos Emeralds and the Master Emerald, I have turned this Death Egg Robot into a Solarian Battle Armor, your most powerful attack will not destroy this mech Sonic. I finally created a indestructible robot not even you could defeat."

"HHAHAHAHAHAHAHAHA"

Eggman finally have done it, he's using Star's wand to enhanced the Death Egg Robot to be indestructible and the Master Emerald and the 6 Chaos Emeralds energy is powering and boosting the wand's magic. What will our heroes going to do?
Star vs the Forces of Evil belong to Disney and Sonic belong to Sega. I don't own anything, sorry if this chapter seems rush but I was trying to give this story a Svtfoe feel. Once again this is my very first fanfiction so my writing is not perfect. This story was originally have 12 chapters with the prologue, but I new to this. In the next Chapter, Seth's real plan begins.